Merge #328

328: Prevent underflow when calling delay(n) with n<2 r=jonas-schievink a=ovidiusabou Calling delay(1) causes a very long wait (freeze) otherwise. 86cd463 introduced this behaviour by changing the cycle count from n / 4 + 1 to n / 2 which forces an underflow when n<2. Co-authored-by: Ovidiu Sabou <ovidiu@sabou.org> Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>
rust-embedded · Feb 9, 2021 · 2281fd6 · 2281fd6
2 parents c714cdf + fdc3ab0
commit 2281fd6
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diff --git a/asm/inline.rs b/asm/inline.rs
@@ -55,7 +55,8 @@ pub unsafe fn __delay(cyc: u32) {
     // The loop will normally take 3 to 4 CPU cycles per iteration, but superscalar cores
     // (eg. Cortex-M7) can potentially do it in 2, so we use that as the lower bound, since delaying
     // for more cycles is okay.
-    let real_cyc = cyc / 2;
+    // Add 1 to prevent an integer underflow which would cause a long freeze
+    let real_cyc = 1 + cyc / 2;
     asm!(
         // Use local labels to avoid R_ARM_THM_JUMP8 relocations which fail on thumbv6m.
         "1:",

diff --git a/bin/thumbv6m-none-eabi-lto.a b/bin/thumbv6m-none-eabi-lto.a
diff --git a/bin/thumbv6m-none-eabi.a b/bin/thumbv6m-none-eabi.a
diff --git a/bin/thumbv7em-none-eabi-lto.a b/bin/thumbv7em-none-eabi-lto.a
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diff --git a/bin/thumbv7m-none-eabi.a b/bin/thumbv7m-none-eabi.a
diff --git a/bin/thumbv8m.base-none-eabi-lto.a b/bin/thumbv8m.base-none-eabi-lto.a
diff --git a/bin/thumbv8m.base-none-eabi.a b/bin/thumbv8m.base-none-eabi.a
diff --git a/bin/thumbv8m.main-none-eabi-lto.a b/bin/thumbv8m.main-none-eabi-lto.a
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